When operated in conjunction with flash or transient illumination, the exposure mechanism of a photographic camera usually is adjusted in accordance with the levels of illumination anticipated at a scene being photographed. To anticipate these levels, an evaluation is made based upon an application of the inverse square law of light energy propagation. Under this law, the light energy available from a given source is considered to vary inversely with the square of the distance from that source. Accordingly, to make an appropriate exposure mechanism adjustment for flash photography, light source-to-subject distance is derived and the value of this distance is utilized to compute an appropriate exposure value or illuminational factor.
In some camera designs, exposure control adjustment for flash operation is effected automatically by incorporating within the apparatus what is termed as a "follow-focus" system. With a follow-focus arrangement, aperture adjustment or flash illumination output control is mechanically coupled with the range finding or focusing system of a camera. In effect, a follow-focus control represents a second exposure control system for a camera. As such, its presence necessarily contributes to the size and complexity of a camera.
Where aperture is adjusted as a follow-focus procedure, the exposure control housing of a camera must incorporate one aperture adjustment mechanism for daylight regulation as well as another control system which is operative exclusively for flash illuminated exposures and which does not otherwise interfere with the daylight exposure regulating system. Providing such dual regulating systems within a fully automated camera and, particularly, a camera which is of such thin and compact design as to be conveniently carried within a pocket of a garment poses complex design considerations.
In one fully automated but thin and compact camera described in U.S. Pat. No. 3,714,879, an exposure control system is described wherein both aperture and exposure interval are automatically varied in accordance with scene lighting conditions. This exposure control system operates in conjunction with a single lens reflex viewing system as well as with a motorized form of automatic film processing. Exposure regulation within the thin, fully automated but compact camera takes place as part of a multi-step program involving the conversion of an optical path between viewing and exposure operational modes.
The shutter-aperture components of the exposure mechanism of the noted reflex camera are normally open for viewing and focusing and are energized to close the taking aperture both for operational mode conversion as well as for terminating exposure interval. An optimized automatic weighting of aperture and exposure interval in accordance with a predetermined program is derived with the control system through the use of a progressively varying aperture movement during any given exposure interval.
A follow-focus control technique for such an exposure control system is described in a U.S. patent entitled, "Focus Responsive Exposure Control System," by Vaito K. Eloranta and Edwin K. Shenk, U.S. Pat. No. 3,750,543, issued Aug. 7, 1973, and assigned in common herewith. The latter application describes a second flash mode control system wherein an electromagnetic device such as a solenoid is selectively maneuvered and energized to extend its plunger and arrest the position of exposure-aperture blades in accordance with focal setting.
A complete follow focus system is described in a U.S. patent entitled, "Apparatus and System for Flash Photography" by Lawrence M. Douglas, issued Aug. 27, 1974, U.S. Pat. No. 3,832,722, and assigned in common herewith. This follow focus system achieves the necessary compactness to meet the overall camera design of the above described variety so as to incorporate both exposure control features within a very compact and thin exposure housing. The above follow focus system additionally provides a "trim" function to accommodate for slight variations in the sensitometric characteristics of the film as well as to insert a modicum of personal or overriding control over the automated system. The trim control has only one control element for operation in this manner reducing the possibility that a camera operator may become confused or overlook a requirement for providing a trim control for that mode of operation which he is currently using.
It is therefore a primary object of this invention to provide for an improved follow focus system of the above described type for a photographic camera apparatus including a uniform trim control whereby a select exposure aperture may be adjusted by a predetermined number of F/stops regardless of the actual camera focus.
It is also an object of this invention to provide an improved follow focus system for photographic camera apparatus which system may be finely adjusted to compensate for the cumulative effect of dimensional variations in the individual components.
It is a further object of this invention to provide an improved follow focus system for a photographic camera apparatus having a trim control adjustable to change a select apparatus opening by a uniform amount regardless of the actual select aperture value as determined by the follow focus system during lens focusing.
Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the mechanism and system possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.